1. Field of the Invention
The present invention is related to a zoom lens system used for a compact video camera, an electronic still camera, or the like.
2. Description of the Prior Art
In recent years, compact video cameras and electronic still cameras having a 1/2 inch or a 1/3 inch screen and a CCD as a light receiving element have been developed.
A taking lens used for these kinds of camera is a compact zoom lens system which has small F-number(it is bright). A retro-focus zoom lens system having 2 lens groups, the first of which has a negative first lens group is known as a conventional compact zoom lens system. However, for a retro-focus type 2 group zoom lens system to make an F aof bout 1:2, the diameter of a lens of a back group must be made obtrusively large. Moreover, high order spherical aberration occurs.
Moreover, a 4 group type zoom lens system is known for use as a small F number zoom lens system. The known 4 group type lens has a positive first lens group, a negative second lens group as a variable power lens, a negative third lens group as a compensator, and a positive fourth lens group as a master lens.
However, the 4 group type zoom lens system has long overall length, and the diameter of a front side lens must be made large.
In a conventional three group zoom lens system, a first lens group or a part of a third lens group (master lens group) is moved along an optical axis in order to adjust a focus.
However, when the first lens group is moved, if the minimum photography distance needs to be shortened, the moving amount of the first lens and the diameter or the lens system are both very large. Moreover, when the third lens is moved, change of an aberration by focusing becomes large.